Lactams for use in the treatment of skin lesions

ABSTRACT

Lactams for use in the treatment of skin lesions are described. In particular, lactams for the treatment of chronic wounds, including chronic wounds in patients having diabetes.

This application is a national phase filing under 35 USC 371 of International Application No. PCT/EP2017/067781, filed on Jul. 13, 2017, which claims priority from EP16180598.1 filed Jul. 21, 2016, the contents of which are incorporated herein in their entirety for all purposes.

FIELD OF THE INVENTION

The invention relates to lactams for use in a method of treatment of skin lesions.

BACKGROUND

Despite advances in antibiotics, persistent infections still present a major problem, especially in the very young, the elderly, and those suffering from certain disorders that compromise the healing process.

Chronic wounds (that is, wounds that do not heal within 12 weeks) represent a particular problem, especially in suffers of diabetes, as these are often complicated by bacterial infections. The occurrence and persistence of bacterial infections typically complicates the healing process. Wounds can become so severe and long standing that the surround flesh undergoes necrosis. Sometimes, excision of the affected tissue or even amputation of the affected digi or part of the limb is eventually required.

Owing to the chronic nature of many of these bacterial infections, long term treatment with antibiotics is often required. Similarly, owing to the danger of chronic wounds conditions, it is common for suffers of conditions such as diabetes to be treated prophylactically, as soon as skin damage is observed or occurs. This long term use of antimicrobial agents can result in bacterial evolution to develop resistance, both within the local environment of a particular patient's wound and the patient population at large.

The emergence of drug-resistant bacteria and fungi presents a significant medical and public health problem. Consequently, there is an urgent need for the development of antimicrobial agents that can overcome drug resistance problems. Bacteria and fungi generally develop drug resistance in four ways: producing metabolizing enzymes for the degradation of the drugs, modifying their targets to render the drugs ineffective, expressing a high level of efflux proteins that “pump” the drug out in order to lower its concentration, and inducing biofilm formation to prevent permeation of drugs into the bacteria.

WO2007/085042 (Biosignal Limited) describes certain lactam structures and their use in the treatment of bacterial infections.

WO2014/118240 (Unilever) describes antimicrobial compositions comprising a lactam and a hydrotrope.

WO2014/183164 (Kumar, Perry and Kit) describes certain N-functionalised dihydropyrrolone compounds and methods for preparing surfaces to which the dihydropyrrolone compounds are attached.

SUMMARY OF THE INVENTION

The invention is based on the inventors' understanding and insight into the unusual biological properties of certain lactam compounds, and the utility of these compounds in methods of treatment owing to their biological profile.

The lactams described herein are antibacterial. Their particular biological profile makes them surprisingly suitable for the treatment of skin lesion infections, in particular in the long term treatment (including prophylactic treatment) of skin lesions. In other words, the lactams may be useful in the treatment of so-called non-healing wounds.

In a first aspect, the invention therefore relates to a lactam for use in a method of treatment or prophylaxis of a bacterial infection of a skin lesion in a subject.

Suitably, the skin lesion is chronic (not healed within 12 weeks) or a skin lesion that is considered at risk of becoming chronic.

Suitably, the infection is a bacterial infection in which Pseudomonas, (usually but not necessarily P. aeruginosa) is implicated.

Suitably, the lactam is a lactam of Formula I or Formula II:

wherein Ar is an optionally substituted phenyl group and R¹ is H or C₁₋₄alkyl.

Accordingly, in a first aspect, the invention may provide a lactam of Formula I or Formula II, for use in a method of treatment of a chronic wound in a subject, wherein Ar is optionally substituted phenyl, said optional substituents being selected from halogen and C₁₋₄alkyl.

In some cases, Ar is unsubstituted. In some cases, Ar is substituted. In this case, each of the 2, 3, 4, 5, and 6 positions may be substituted or unsubstituted. For example, Ar may be 2,4-disubstituted, 3,4-disubstitued, 2,4,6-trisubstituted, 3,4,5-trisubstituted, 2,3,4-trisubstituted, 2,4,5-trisubstituted, etc.

Suitable substituents R² include halogen, C₁₋₄alkyl, OH, C₁₋₄alkoxy, CF₃, OF₃.

In some cases, Ar has a substituent at the 4-position. In some cases, the substituent at the 4-position is chloro, fluoro or methyl, optionally chloro or methyl.

For example, Ar may be

where n is 0, 1, 2, 3, or 4, preferable 0 or 1, most preferably 0.

Preferably, the lactam is a lactam of Formula Ia or Formula IIa:

wherein

R¹ is H or C₁₋₄alkyl (preferably methyl);

R² is selected from H, halogen, C₁₋₄alkyl, OH, C₁₋₄alkoxy, CF₃, OF₃.

In some cases, the lactam is a lactam of formula Ia. In some cases, the lactam is a lactam of formula Ila.

Preferably, R¹ is H.

Preferably, R² is halogen (preferably, F, Cl, or Br), or C₁₋₄alkyl (preferably methyl).

Preferably, R² is halogen. Halogen includes F, Cl, Br, and I. For example, R² may be fluoro or choro, for example chloro.

Preferred lactams may include:

Especially preferred lactams include: 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488); 5-methylene-4-(p-tolyl)pyrrol-2-one (Ref. 491); and 4-(4-fluorophenyl)-5-methylene-pyrrol-2-one (Ref. 310).

The lactams may be useful for the treatment of a variety of chronic skin lesion in a subject, but may be especially useful for the treatment of diabetic ulcers, for example diabetic foot ulcers.

The lactams of Formula I and II act to prevent the formation of, retard or prevent the growth and development of, and/or reduce the extent of a bacterial biofilm. The present invention thus includes lactams of Formula I and II for use in the treatment of a bacterial infection in a subject by preventing the formation of, retarding or preventing the growth and development of, and/or reducing the extent of a bacterial biofilm. Pseudomonas, typically P. aeruginosa, may be implicated in the bacterial biofilm.

In the present invention, the subject being treated is preferably a mammalian subject and most preferably a human.

While the lactams may be used for treatment in a variety of subjects having chronic skin lesion, an advantage of the methods described herein is the unusual biological profile of the lactams, which may make the lactams especially suitable for the treatment of diabetic patients. Accordingly, in some cases, the subject is diagnosed as having diabetes. The diabetes may be Type I or Type II.

In some subjects, and particularly in subjects diagnosed as having diabetes, the lactams may be used prophylactically for preventing the occurrence or recurrence of a bacterial infection of a skin lesion, even when the skin lesion is not definitely chronic.

The lactams of Formula I and II may be used as the first line of treatment of a skin lesion infection, or may be used in subjects already treated with other antibiotics for the same infection, for example those who have not shown a satisfactory response to those other antibiotics.

If appropriate, the lactams of Formula I and II may be administered together with other treatments, including other antibiotic treatments.

In a second aspect, the invention provides a method of treatment of a bacterial infection of a skin lesion, the method comprising administering to a subject a therapeutically effective amount of a lactam of Formula I or Formula II.

In a third aspect, the invention provides the use of a lactam of Formula I or Formula II in the manufacture of a medicament for the treatment of bacterial infections of skin lesion.

In a fourth aspect, the invention provides a pharmaceutical composition comprising a lactam of Formula I or Formula II, wherein the composition is formulated for topical administration to the skin, for example as cream, gel or lotion.

It will be appreciated that all preferences described with respect to the first aspect apply similarly to the second, third, fourth aspects, as appropriate.

DETAILED DESCRIPTION

The invention will now be described with reference to the following drawings in which:

LB medium=Lysogeny broth ex. Sigma Aldrich UK.

Lactam 131=4-phenyl-5-hydroxy-5-methyl-1H-pyrrol-2-one

Lactam 258=4-(4-fluorophenyl)-5-hydroxy-5-methyl-1H-pyrrol-2-one

Lactam 310=4-(4-fluorophenyl)-5-methylene-pyrrol-2-one

Lactam 316=4-(4-bromophenyl)-5-hydroxy-5-methyl-1H-pyrrol-2-one

Lactam 488=4-(4-chlorophenyl)-5-methylene-pyrrol-2-one

Lactam 491=5-methylene-4-(p-tolyl)pyrrol-2-one

and

FIG. 1 shows a comparison of the expression of P. aeruginosa lasI::lux in the presence and absence of lactams 131, 258, 316, 488 and 491 at 100 μM. Control—LB medium+1% methanol.

FIG. 2 shows a comparison of the expression of P. aeruginosa rhlI::lux in the presence and absence of lactams 131, 258, 316, 488 and 491 at 100 μM. Control—LB medium+1% methanol.

FIG. 3 shows a comparison of the expression of P. aeruginosa pqsA::lux in the presence and absence of Unilever lactams 131, 258, 316, 488 and 491 at 100 μM. Control—LB medium+1% methanol.

FIG. 4 shows a comparison of the expression of P. aeruginosa tac::lux in the presence and absence of Unilever lactams 131, 258, 316, 488 and 491 at 100 μM. Control—LB medium+1% methanol.

FIG. 5 shows vials demonstrating pyocyanin production by PAO1-L grown in the presence of lactam 488 in 0 (1), 100 (2) and 10 μM (3). (4) is an LB only control.

FIG. 6 shows the effect of lactam 488 on the expression of pqsA::lux in P. aeruginosa PAO1-L.

FIG. 7 shows the effect of lactam 491 on expression of pqsA::lux in P. aeruginosa PAO1-L.

FIG. 8 shows the effect of PQS on the expression of pqsA::lux in PAO1-L ΔpqsA in presence of lactam 488 EC₅₀ for PQS increased from 2 μM to 31 μM in the presence of 488 (215 μM).

FIG. 9 shows the effect of 488 at 0, 50, 100, 200 μM on the PQS-dependent expression of pqsA′::lux in P. aeruginosa PAO1-L ΔpqsA. The data show that PQS competes with 488 for PqsR-dependent activation of pqsA::lux fully restoring light output in the presence of 50 μM but not 100 μM or 200 μM of 488.

FIG. 10 shows the effect lactam 488 on the expression of pqsA′::lux in PAO1ΔpqsA in the presence of PQS at 0 μM, 10 μM or 40 μM.

FIG. 11 shows the PqsR-independent activity of 488 on the expression of pqsA′::lux in PAO1-N ΔpqsAHR.

FIG. 12 shows the inhibitory effect of 488 on the expression of pqsA′::lux in P. aeruginosa.

FIG. 13 shows TLC analysis of HHQ production. (Panel A) TLC plate under UV light at 312 nm, showing PQS (lane 1 upper spot) and HHQ (lane 1 lower spot) standards together, 488 standard (lane 2), organic solvent supernatant extracts of PAO1-N ΔpqsAHR grown without (lane 3) and with (lane 4) the compound 488 and organic solvent supernatant extracts of PAO1-N ΔpqsAHR pqsABCD grown without (lane 5) and with 488 (lane 6). Pyocyanin production (Panel B) and light output (Panel C) occurs via PAO1-L ΔpqsA CTX::pqsA′-luxCDABE present in the agar overlay. Both pyocyanin and light output are dependent on the presence of AQs. Bioluminescence was captured using a luminograph photon camera. The uppermost bright spot on the UV illuminated plate (Panel A, lanes 2, 4 and 6) is 488.

PSEUDOMONAS AERUGINOSA

Pseudomonas aeruginosa is a pathogen important in certain bacterial skin infections and is associated with severe and often chronic infections in chronic wounds. There are a number of P. aeruginosa strains, including PA01, PA7, USBPP-PA14 and strain 2192. Except where indicated otherwise, a reference to P. aeruginosa is intended to refer to any and all strains.

The methods described herein may be directed to treatment of infections in which P. aeruginosa is implicated. The P. aeruginosa may be a strain that produces AQs (alkylquinoline compounds). The P. aeruginosa may be a strain that produces one or both of PQS (Pseudomonas quinolone signal; 2-heptyl-3-hydroxy-4-(1H)-quinolone) and HHQ (4-hydroxy-2-heptylquinoline). The P. aeruginosa may be a strain belonging to one of the two major P. aeruginosa genomic groups (PAO1 and PA14).

Skin Lesions

As used herein, the term skin lesion refers to a wound or sore resulting from, for example, an injury, other skin trauma or a pathological cause such as restricted blood circulation. Examples of skin lesions include areas where the skin has been torn, cut or punctured, ulcers (from pre-ulcerative lesions to gangrenous tissue).

Skin lesions may affect only the epidermis and dermis, or they may affect tissues all the way to the fascia.

Quorum Sensing

Quorum sensing (QS) is a mechanism whereby microorganisms, and in particular bacteria, communicate with each other and exhibit community-wide behaviour coordination through the secretion and detection of chemical signals called autoinducers (AIs). Quorum sensing has been demonstrated in a large number of bacteria species/strains and important in regulating bacterial virulence, drug resistance, expression of efflux transporters, and biofilm formation, and therefore is attracting attention in the antimicrobial field. (Frontiers in microbiology 6 (1036) September 2015).

Quorum sensing is a cell-density based intercellular communication system to regulate collective behaviour, which plays a key role in regulation of bacterial virulence and biofilm formation. The process relies on the production, release and group-wide detection of signal molecules called autoinducing peptides (AIPs), which in gram-negative bacteria are typically homoserine lactones, (HSLs), especially N-acyl-homoserine lactones (AHLs). Other quorum sensing molecules are known, including epinephrine/norepinephrine.

Biofilm formation enables the bacteria to resist antibiotics because once the bacteria sense that the outer layer of the biofilm is being destroyed, the inner layers will grow stronger to re-establish the community. The present invention is based on the inventors' investigation into the properties of certain lactams as described herein and their insight into the way in which said lactams influence QS in gram negative bacteria such as P. aeruginosa.

The QS network of P. aeruginosa is organised in a multi-layered hierarchy consisting of at least four interconnected signalling mechanisms and demonstrates plasticity, in that it can respond to bacterial population changes and possibly also environmental stress cues. P. aeruginosa orchestrates biofilm formation—and production of virulence factors—by reliance on two QS systems, both part of the Luxl/R signalling cascade, the Las and Rh1 systems.

In Pseudomonas aeruginosa, the acyl-homoserine lactone (AHL) and alkyl quinolone (AQ) QS systems are important for virulence and biofilm formation. One acyl-HSL QS regulator is LasR. A non-AHL signalling molecule produced by P. aeruginosa is known as PQS (Pseudomonas quinolone signal), which is 2-heptyl-3-hydroxy-4-(1H)-quinolone.

Biofilm

The term “biofilm” as used herein refers to biological films that develop and persist at interfaces in aqueous environments. These biological films are composed of microorganisms embedded in organic gelatinous matrices composed of one or more matrix polymers that are secreted by the resident microorganisms. Biofilms can develop into macroscopic structures and are also capable of trapping nutrients and particulates that can contribute to their enhanced development and stability. Biofilms can also prevent penetration of antimicrobial agents, which may lead to persistent infections. Formation of biofilms provides bacteria with a protected environment such as within a partially healed and/or covered wound with can withstand various stresses, including many antibiotic treatments.

Pharmaceutical Compositions

The invention further provides pharmaceutical compositions comprising a lactam as described herein. It will be appreciated that the pharmaceutical composition will be formulated to be suitable for the intended route of administration. A pharmaceutical composition comprising a lactam of Formula I or II will typically include a pharmaceutically acceptable carrier and may optionally include other therapeutic ingredients.

Suitably, the composition is formulated for topical administration to the skin, for example, as a cream, gel or lotion. In some cases, systemic administration may also be used, for example, intravenously. According, in some cases, the composition is formulated for parenteral administration.

Preferably the composition is formulated to provide an effective amount of the lactam. The term “effective amount” as used herein refers to an amount of the lactam at least sufficient to achieve a desired modulation of the activity or physiological property of a microbial population. The effective amount is determined, at least in part, upon the compound used, the microbial species present, the structure, system, or host, and the desired level of regulation. Modulating the activity or physiological property of the microbial population includes, but is not limited to, slowing, attenuating or inhibiting the growth of a microbial population and/or the colonization of a surface; causing a partial or total reduction in a microbial population; inhibiting the formation, development or growth of a biofilm, and partially or totally reducing the extent of a biofilm, and the like.

Methods of Treatment

It will be appreciated that the term “methods of treatment” as used herein includes prophylaxis, treatment that hamper bacterial colony population growth, treatments that keep a bacterial colony population stable, and treatments that reduce or eradicate a bacterial population.

The invention relates to methods of treatment for skin lesion infections. These are commonly referred to as non-healing wounds. A chronic condition is characterised by long duration or frequent recurrence, typically where a wound has not healed within 12 weeks of first occurrence.

Chronic bacterial wound infections present a particular problem in diabetes sufferers. Accordingly, the present invention is envisaged for the treatment of bacterial skin lesion infections in patients that have been diagnosed with diabetes.

Owing to their unusual biological profile, the lactams of Formula I and II may be useful in the long term treatment of infections. This is because, owing to their selective interactions with the various bio-pathways of the bacteria, and in particular P. aeruginosa, the lactams may permit population control and reduction without triggering the mechanisms that are thought to lead to evolutionary resistance.

In some cases, the bacterial infection is an infection in which Pseudomonas, (usually but not necessarily P. aeruginosa) is implicated.

The methods described herein may be suitable for long term use. Accordingly, the methods may include regular administration of the lactam to a subject for a period of at least several weeks, several months, at least one year, at least two years, at least three years, at least 5 years, at least 8 years, or at least 10 years.

EXAMPLES

To elucidate the mechanism of action of compounds described herein, the impact of each lactam on both N-acylhomoserine lactone (AHL) and 2-alkyl-4-quinolone-(AQ)-dependent quorum sensing (QS) in P. aeruginosa was explored.

The expression of rhl and las AHL- and the pqsA AQ-synthase genes was evaluated using lux-based lasI (FIG. 1), rhlI (FIG. 2) and pqsA (FIG. 3) chromosomally integrated promoter fusions. Luminescence was quantified as a function of bacterial growth. The applicant further determined that none of the lactams is growth inhibitory at 100 μM using a large number of strains (figure not shown).

The P. aeruginosa PAO1-N tac::lux strain was used as a positive control biosensor as it constitutively expresses luxCDABE and hence light (FIG. 4). Any reduction in light output in this strain in the presence of a lactam will show whether or not the compound has an adverse effect on luminescence per se. The tac::lux expression profile shows that there is no interference between the compounds and the enzymes involved in light generation. Any effects observed on incubation of the QS reporter strains with the lactams will therefore be due to alterations in promoter expression.

The qualitative effect of compound 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) on pyocyanin production by PAO1-L was then investigated.

Pyocyanin is a blue redox-active secondary metabolite and a putative signalling molecule in P. aeruginosa (Jayaseelan et al, 2014). The pyocyanin biosynthetic (phz) genes are regulated by QS and in part via the transcriptional regulator PqsR acting through PqsE (Rampioni et al 2011). Pyocyanin production was visually assessed after 8 h of incubation at 37° C. in P. aeruginosa strain PAO1-L in the presence and absence of compound 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488), which FIG. 3 shows was the most potent inhibitor of the PqsR-dependent pqsA::lux promoter fusion. FIG. 5 shows the culture supernatants of PAO1-L grown in the absence or presence of lactam 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488).

The inhibition of pyocyanin production by lactam 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) was observed as the absence of green pigmentation in culture supernatant in vial 2 (FIG. 5). Although qualitative, this observation offers further confirmation of the inhibitory effects of lactam 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) on AQ-dependent QS.

The inhibitory properties of compounds of the invention on AQ-dependent QS in P. aeruginosa were then investigated.

In P. aeruginosa, the pqsABCDE genes code for the biosynthetic pathway required for the synthesis and action of 2-alkyl-4(1H)-quinolones (AQs) (Heeb et al 2010). The transcriptional activator PqsR regulates the expression of the pqs biosynthetic pathway that in turn controls secondary metabolites such as elastase, pyocyanin and phospholipase as well as biofilm maturation and swarming motility. In this QS system, the primary AQ signal molecules are 4-hydroxy-2-heptylquinoline (HHQ) and 2-heptyl-3-hydroxy-4-quinolone (PQS) both of which act as co-inducers of PqsR (Heeb et a12010; Ilangovan et al 2013).

The results from the first screening experiments (FIG. 1-3) using AHL and AQ biosensor strains clearly show that inhibition of the pqs-system is the main effect of lactams 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) and 5-methylene-4-(p-tolyl)pyrrol-2-one (Ref. 491) on QS in P. aeruginosa. To determine the relative inhibitory activities (IC_(50s)) of 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) and 5-methylene-4-(p-tolyl)pyrrol-2-one (Ref. 491), dose response curves were constructed using the same biosensor strain (P. aeruginosa PAO1 pqsA::lux; Fletcher et al, 2007; Ilangovan et al 2013). This strain produces light in response to the endogenous production of AQs such as PQS and HHQ. The data obtained are presented in FIG. 6 and FIG. 7 from which IC_(50s) were calculated as 22 μM for 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) and 44 μM for 5-methylene-4-(p-tolyl)pyrrol-2-one (Ref. 491) respectively. While 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) is the more potent of the two compounds, 5-methylene-4-(p-tolyl)pyrrol-2-one (Ref. 491) showed the desired effect. It can also be seen that 5-methylene-4-(p-tolyl)pyrrol-2-one (Ref. 491) did not inhibit pqsA expression as strongly as 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) at high concentrations while 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) completely inhibited light output and hence pqsA expression.

FIGS. 6 and 7 demonstrate the binding and inhibition of the PQS quorum sensing in pseudomonas, with compound 488 showing the ability to fully knock out the PQS. The 491 compound in FIG. 7 whist proving inhibition did not give complete knock out at higher concentration.

The mode of action on AQ-dependent QS was investigated.

The major QS molecules in the pqs system are the AQs, PQS and its precursor HHQ (Williams & Camara 2009). Their biosynthesis requires the regulator PqsR and the biosynthetic proteins, PqsABCD and the mono-oxygenase, PqsH (Heeb et al 2010).

The inhibitory action of 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) may involve inhibition of AQ biosynthesis or 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) may behave like an antagonist and block the PQS receptor, PqsR. These experiments do not discriminate between inhibition of PqsR activation and inhibition of AQ biosynthesis because the biosensor strain used maintains an intact AQ-dependent QS system. Experiments were therefore designed to determine the nature and degree of 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) inhibitory activity. Firstly, the possibility that 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) is an inhibitor of the response regulator protein, PqsR that is essential for expression of the pqsABCDE genes and hence AQ production was explored.

By using the AQ-non producing P. aeruginosa strain PAO1-L ΔpqsA, pqsA::lux, the EC₅₀ value for the native PqsR agonist, PQS was calculated as ˜2 μM (Ilangovan et al. 2013). In the presence of a fixed concentration of lactam 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) and a range of PQS concentrations, the EC₅₀ value increased ˜15 fold to 31 μM (FIG. 8). This suggests that 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) acts as a competitive antagonist of AQ signalling potentially inhibiting the interaction between PqsR and its co-inducer, PQS.

The experiment shown in FIG. 8 was then repeated using 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) concentrations of 0, 50, 100 and 200 μM. The results obtained are shown in FIG. 9 which shows that as 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) concentrations are increased, maximal light output is substantially reduced. The shape of the dose response curves indicates that 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) is a competitive antagonist as increasing the PQS concentration, restores pqsA::lux expression.

These data demonstrate the selective binding and competitive antagonist activity of 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488).

A PAO1-L ΔpqsA pqsA′::lux biosensor-based assay was performed to determine whether lactam 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) exhibits any partial agonist activity at higher concentrations. A partial agonist is a molecule that can bind to and activate a receptor resulting in a non-complete response compared with a full agonist. Graphically, an antagonist that is also a partial agonist exhibits agonist activity at high concentrations. FIG. 10 shows that 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) has no partial agonist activity as it was unable to activate pqsA expression at concentrations up to 800 μM. This contrasts with its activity as an antagonist in the presence of 10 or 40 μM PQS. This demonstrates that at higher concentrations there is no activation of receptor binding, offering low or even no toxicity at higher doses.

PQS is capable of weakly activating pqsA in the absence of PqsR via a mechanism that is not fully understood but appears to depend on the iron chelating properties of PQS. The aim of this experiment was to clarify whether lactam 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) is also inhibitory for pqsA expression via the PqsR independent pathway. As previously described, the pqsA′::lux biosensor based on the triple mutant PAO1-N ΔpqsAHR cannot produce AQs and lacks pqsR but still responds to exogenous PQS. This response is however much weaker that the PqsR-dependent response. FIG. 11 shows the impact of 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) on the PqsR-independent expression of pqsA in the presence or absence of 40 μM PQS. 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) has a small inhibitory effect on the PqsR-independent pathway. This suggests that while the compounds of the invention may have some effect on P. aeruginosa that do not express AQs, they show most promise for in the treatment of disorders in which AQ-producing strains are implicated.

Indeed for 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) the PQS pathway is the dominant inhibitory route. Taking into account the role of quorum sensing in toxicity and virulence of pseudomonas, then this technology is most effective against those strains capable of quorum sensing.

To investigate the inhibitory effect of 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) on P. aeruginosa PA14, a pqsA′::lux fusion was introduced onto the chromosome. Comparable inhibitory effects with those previously described for strain PAO1 were observed. The IC₅₀ extrapolated from the inhibition curve in FIG. 12 was calculated to be 17.9 μM.

To determine whether 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) is capable of inhibiting the enzymes (PqsABCD) involved in AQ biosynthesis, the P. aeruginosa PAO1-N ΔpqsAHR was exploited. This mutant cannot produce AQs because the genes coding for the key biosynthetic enzymes (PqsA and PqsH) and regulation (PqsR) have been deleted. To restore AQ production in a PqsR-independent manner in PAO1-N ΔpqsA, the pqsABCD genes were introduced on a plasmid (pBBR pqsABCD; Niewerth et al. 2011). P. aeruginosa PAO1-N ΔpqsAHR and P. aeruginosa PAO1-N ΔpqsAHR pBBR pqsABCD were both incubated overnight in LB with and without 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) (200 μM), resuspended to an OD₆₀₀ 1.0. The cultures were extracted with acidified ethyl acetate, the organic phase removed, dried and resuspended in methanol subjected to thin layer chromatography (TLC).

TABLE 1 1 PQS, 10 mM + HHQ, 10 mM, 2 μl 2 488 10 mM, 5 μl 3 PAO1-N ΔpqsAHR organic extract, 10 μl 4 PAO1-N ΔpqsAHR + 488 200 μM organic extract, 10 μl 5 PAO1-N ΔpqsAHR pBBR-pqsABCD organic extract, 10 μl 6 PAO1-N ΔpqsAHR pBBR-pqsABCD + 488 200 μM organic extract, 10 μl

After chromatography using a dichloromethane-methanol mobile phase, the TLC plates were overlaid with a thin agar layer containing the AQ biosensor strain PAO1-L ΔpqsA CTX::pqsA′-luxCDABE (Fletcher et al. 2007) incubated and examined for reporter output (FIG. 13). FIG. 13 panel A shows the TLC plate under UV illumination after chromatography. The biosensor strain produces light (FIG. 13 panel C) and pyocyanin (FIG. 13 panel B) in response to AQs that bind to PqsR and activate the pqsA promoter.

The biosensor revealed the presence of HHQ both in the samples of PAO1-N ΔpqsAHR pBBR-pqsABCD without (FIG. 13 panels B and C; lane 5) and with (FIG. 13 panels B and C lane 6) compound 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one (Ref. 488) indicating that the lactam did not inhibit HHQ biosynthesis.

Sources of Bacterial Strains

The bacterial strains were obtained or made as follows:

TABLE 2 Strain Antibiotic Source or reference Escherichia Coli: S17-1 pMiniCTX-pqsA::lux Gentamycin 25 μg/ml Diggle et al., 2007 DH5 pBBRMCS-5::pqsABCD Gentamycin 25 μg/ml Niewerth et al., 2011 Pseudomonas aeruginosa: PAO1-L — Halloway collection PAO1-N — Halloway collection PAO1-L ΔpqsA — This study PAO1-L ΔpqsA, pqsA::lux Gentamycin 25 μg/ml This study PAO1-N ΔpqsA — Aendekerk et al., 2005 PAO1-N ΔpqsA, pqsA::lux Tetracyclin 125 μg/ml Diggle et al., 2007 PAO1-N ΔpqsAH Diggle et al., 2007 PAO1-N ΔpqsAH, pqsA::lux Gentamycin 25 μg/ml Diggle et al., 2007 PAO1-N ΔpqsAHR Ilangovan at al., 2013 PAO1-N ΔpqsAHR, pqsA::lux Gentamycin 25 μg/ml By applicant PAO1-L ΔpqsAHR, pqsABCD Gentamycin 25 μg/ml By applicant PAO1-L ΔrhlI — Dr. Matthew Fletcher PAO1-L ΔlasI — Dr. Matthew Fletcher PAO1-L pqsA::lux Gentamycin 25 μg/ml By applicant PAO1-L las::lux Gentamycin 25 μg/ml James Lazenby. Unpublished′ PAO1-L rhlI::lux Gentamycin 25 μg/ml James Lazenby. Unpublished′ PAO1-N tac::lux Tetracyclin 125 μg/ml By applicant PA ATCC 15442 — Unilever* PA ATCC 15442, pqsA::lux Gentamycin 25 μg/ml By applicant PA14 Rahme et al., 1995 PA14, pqsA::lux Gentamycin 25 μg/ml By applicant *accession no. AYUC00000000 on DDBJ/EMBL/GenBank

Summary of Biological Activity

The examples demonstrate that compounds of the invention have been shown to:

-   -   inhibit alkylquinolone (AQ) dependent quorum sensing (QS) in P.         aeruginosa.     -   inhibit PqsR in representative strains belonging to the major P.         aeruginosa genomic groups (PAO1 and PA14 respectively).     -   interact antagonistically with the LysR-type regulator PqsR (in         a competitive manner without partial-agonist activity).     -   do not appear to directly inhibit AQ biosynthesis but block AQ         synthesis by acting as a PqsR antagonist.     -   potentially interact with the co-inducer binding domain of PqsR         (PqsR^(CBD)) acting an allosteric inhibitors.

This provides an unusual biological profile that may enable compounds of the invention to be useful in the treatment of chronic wounds complications stemming from bacterial infection. In particular, the biological profile of the compounds of the invention offer utility in the treatment of chronic wounds experienced by diabetes patients. This is because the compounds of the invention have a biological activity profile that controls multiplication and biofilm formation, but does not trigger the bio-pathways that are associated with developing antibacterial resistance.

REFERENCES

The references cited herein are incorporated by reference in their entirety for all purposes:

-   Aendekerk S, Diggle S P, Song Z, Høiby N, Cornelis P, Williams P,     Camara M. The MexGHI-OpmD multidrug efflux pump controls growth,     antibiotic susceptibility and virulence in Pseudomonas aeruginosa     via 4-quinolone-dependent cell-to-cell communication. (2005)     Microbiology 151(4) 1113-25. -   Fletcher M P, Diggle S P, Camara M & Williams, P. (2007)     Biosensor-based assays for PQS, HHQ and related 2-alkyl-4-quinolone     quorum sensing signal molecules. Nature Protocols, 2, 1254-1262     doi:10.1038/nprot.2007.158. -   Fletcher M P, Diggle S P, Camara M. and Williams P. (2007)     Biosensor-based assays for PQS, HHQ and related 2-alkyl-4-quinolone     quorum sensing signal molecules. Nature protocols, 2, 1254-62. -   Freschi et al. (2015) Clinical utilization of genomics data produced     by the international Pseudomonas aeruginosa consortium. Frontiers in     microbiology 6, Article 1036. -   Ilangovan A, Fletcher M, Ramioni G, Pustelny C, Rumbaugh K, Heeb S,     Camara M, Truman A, Chhabra S R, Emsley J & Williams P. (2013)     Structural basis for native agonist and synthetic inhibitor     recognition by the Pseudomonas aeruginosa quorum sensing regulator     PqsR (MvfR). PLOS Pathogens 9(7):e1003508. -   Niewerth H, Bergander K, Chhabra S, Williams P, and     Fetzner S. (2011) Synthesis and biotransformation of     2-alkyl-4(1H)-quinolones by recombinant Pseudomonas putida KT2440,     Applied Microbiology and Biotechnology, 91, 1399-1408. -   Rahme L G, Stevens E J, Wolfort S F, Shao J, Tompkins R G, et     al. (1995) Common virulence factors for bacterial pathogenicity in     plants and animals. Science, 268: 1899-1902. 

The invention claimed is:
 1. A method of treatment of a bacterial infection of a skin lesion in a subject comprising: administering to the subject an effective amount of 4-(4-chlorophenyl)-5-methylene-pyrrol-2-one; wherein the bacterial infection is caused by Pseudomonas.
 2. The method of claim 1, wherein the skin lesion is a chronic skin lesion.
 3. The method of claim 1, wherein the subject has diabetes. 